Clock Ensemble Algorithm Test in the Establishment of Space-Based Time Reference
Round 1
Reviewer 1 Report
Review: Analysis of establishing satellite-based time reference
remotesensing-2145529-peer-review-v1.pdf. Jan 5, 2023
The authors discuss the possibility of establishing a highly accurate future satellite-based time reference. They test three Kalman filter methods for composite clock stability and prediction using 5-months of GFZ clock correction data with three GNSS constellations (BDS, GPS, and Galileo) each using a variety of onboard clocks. Although the onboard clock test results are not new, they help validate the testing. This is a good first step in establishing the future satellite-based time reference and should be of interest to the composite clock time research community. The paper is generally well written. I recommend publication after the authors respond to the few comments found in the attached annotated manuscript.
Comments for author File: 
Comments.pdf
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 2 Report
Remote sensing is a new field of research that enters our lives. The authors made a lot of effort but did not discuss many aspects. I believe they should refer to similar publications such as https://doi.org/10.3390/rs14051281 The article is about a digital elevation model (DEM) is an essential element of input data in the model research of watersheds. The study, gradually and with various methods, carried out a great simplification of a detailed LiDAR-derived DEM. Then, the impact of that treatment on the precision of the selected elements for modeling a watershed was assessed. The simplification comprised a reduction in resolution, with the use of statistical resampling methods, namely giving an average, modal, median, minimum, maximum, or the closest value to the pixels.
Author Response
We thank the reviewer for providing quick feedback on our manuscript. But we feel confused about the recommended reference, since DEM (Digital Elevation Map) will not be used in the process of establishing the space-based timescale discussed in our manuscript. We are afraid that there might be some misunderstandings.
Reviewer 3 Report
My comments can be found in the uploaded file Review_Comments-2023-01-26.pdf.
Comments for author File: Comments.pdf
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 4 Report
The methodology is applicable and the results are clear. It would be nicer if the authors find a local English speaker polishing the article and the quality of research is stamped. Examples are
1. Does the title (Satellite-based time reference analysis) read better?
2. Discussion and Conclusion (part 5) are usually presented. The order is introducing the concept, and following the introduction, then the benefit can be seen.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
The current manuscript has been greatly improved after the authors’ revision. While few of my comments have not been corrected although I have marked in red. Please pay attention to the highlight word in my comments. In addition, many phrases are not clear enough.
Two recommendations for the authors: 1)marking the revisions in different colors according to the comments from different reviewers and 2) updating the line number in the responses according to your revised manuscript.
My detailed comments are given as follows.
1. Line 164: “every clock is equivalent”, this sentence is a little bit misleading to the author. It seems that the clocks have the same values. If it was, may be the word ‘identical’ is more appropriate.
2. Line 168: I cannot find the links between the sentence ‘The ? matrix has to be changed’ and the context.
3. Line 186: “the phase error variance in error covariance matrix P diverges strongly”, this sentence is verbose and confusing. First of all, the phrase ‘error variance’ is not formal, the variance of phase error may be more precise. Also, it reads like the variance diverges, do you mean the solution/state vector of phase error diverges?
4. Line 211: I think the ‘deviation’ is a plural noun based on the context here. Or the authors may double-check the phrase ‘N-1 time deviation(s)’.
5. Line 253: ‘..., so that …’ may be replaced by ‘, therefore…’.
6. Line 305-307: this sentence is not well-written. The authors may rephrase to make it clear.
7. Line 436-437: “There are many kinds of clock deviation prediction models, including quadratic polynomial model, gray model, Kalman filter model, and so on Their accuracy is of a similar magnitude” can be rephrased as “Many prediction models of clock deviation have been developed with similar accuracy, e.g., the quadratic polynomial model, the gray model, and the Kalman filter model.”
8. Figure 8: I may not make it clear in my previous comments. I think the authors can apply the unit of ns to y-axis directly as that has been done in Figure 9.
9. Line 537: “The results show that NKT and RKT are similar when …”, this sentence is obscure. Do you mean “the accuracy of NKT and RKT are close”?
10. Line 538: change ‘while’ to ‘although’.
11. Line 539: “In addition, …for on-board clocks, so …” may be rephrased as “Since, …on-board the satellites, hydrogen clocks…”.
12. Line 541: “Then, we use…” to “In addition, we use…”.
13. The authors are recommended to further polish the abstract and conclusions as these are two critical sections of the paper.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
